The pulp and paper industry, as well as other process industries, employs chemical reactions in processes that are often performed in vessels under pressures greater than atmospheric pressure. Such vessels are referred to as pressure vessels. Typically, these processes are performed within pressure vessels that maintain the product at predetermined super-atmospheric pressures and at elevated temperatures which promote the desired chemical reaction. Continuous or batch pulp digester vessels are examples of pressure vessels within which chemical reactions are performed under elevated pressures and temperatures to produce pulp from lignocellulosic material, including but not limited to wood chips, comminuted cellulosic material, biomass, etc.
The processes being performed often require agitation or stirring of the lignocellulosic material in the pressurized digester vessel, especially during a chemical reaction. Such agitation or stirring could also assist in the discharge of treated material from the digester vessel while the lignocellulosic material is under pressure and at elevated temperatures. The agitation is typically effected by a shaft-driven agitator. An electric motor drives the shaft via a power transfer device, such as a transmission, which may include belts, drive chains and a gear reducer. Hydraulic drive systems for vessels are described in U.S. Pat. No. 7,846,298. Hydraulic devices are good for slow rotation applications, such as low rpm (revolutions per minute) and high torque applications. These applications include stirring devices for continuous digester vessels.
Hydraulic drive systems were previously fixed directly to the housing of an existing pressurized digester vessel. Typically, a bell housing at the bottom of the digester vessel provided a mount for the housing of the hydraulic drive system. The coupling between the housings resulted in significant torsional loads being applied to the housing of the pressurized digester vessel. Further, attaching the housing of a hydraulic drive to older digester vessels was difficult because the equipment, such as an outlet device of a digester vessel is formed of iron and cannot be modified by welding i.e., modified by welding an adapter flange.
Adding a hydraulic drive system to an existing pressurized digester vessel, originally having a gearbox, speed reducer, or other mechanical transmission device, typically required configuring the housing of either the hydraulic drive system, the bell housing, or another appropriate system. The configuration would take place at the bottom of the pressurized digester vessel and ensure the housings could be fastened together. Such fastening is important as the original pressurized digester vessels were typically made out of materials where welding could not be utilized. Further, the outlet device drive shaft typically had to be configured to conform to the hydraulic drive which often required a new shaft. In addition, the foundation below the pressurized digester vessel, which supports the mechanical transmission and motor assembly, had to be manipulated or otherwise removed in connection with the removal of the mechanical transmission and motor assembly. Such manipulation would require significant resources and expense in order to appropriately alter the foundation without damaging the integrity of the foundation, as this is the foundation for the digester vessel.
What is needed is a hydraulic drive assembly capable of providing the desired rpm and torque necessary to power a digester, while being mounted to a non-weldable surface. Such an assembly could be inserted into the already-existing foundation envelope and mounted to the non-weldable surfaces of the digester and attached to the sole plates. Such a system would have the advantage of providing adequate rpm and torque while improve safety factors and reduce system breakdown. In addition, hydraulic drive systems and the resulting mounting assembly could result in a reduction of area used in the foundation envelope allowing the unused space to be used to maintain the hydraulic drive assembly.